G. Lamanna

Universität Stuttgart · Institute of Aerospace Thermodynamics

With technical progress, combustion pressures have been increased over the years, frequently exceeding the critical pressure of the injected fluids. For conditions beyond the critical point of the injected fluids, the fundamental physics of mixing and evaporation processes is not yet fully understood. In particular, quantitative data for validation...

The existence of large-scale turbulent structures within a porous medium, generated through the interaction with a turbulent outer flow, is a highly debated topic, albeit most of the analysis is based on computational studies. This study contributes to the ongoing discussion by providing detailed point-measurements of the velocity in both regions b...

The influence of surface roughness, especially regularly patterned micro-structures on the physical outcomes of droplet impacts, is far from fully understood. In order to get a deeper insight into the physics of the impact phenomena, a systematic experimental study of the morphology on regularly patterned micro-structured surfaces has been carried...

Collisions between a stream of drops and a continuous jet of a different liquid are experimentally investigated. In contrast to previous studies, our work focuses on the effects of liquid miscibility and wettability on the collision outcomes. Thus, miscible and immiscible liquids providing total and partial wetting are used. We show that, as long a...

Physics of supercritical fluids is extremely complex and not yet fully understood. The importance of the presented investigations into the physics of supercritical fluids is twofold. First, the presented approach links the microscopic dynamics and macroscopic thermodynamics of supercritical fluids. Second, free falling droplets in a near to supercr...

The development of combustion processes to achieve higher efficiencies has led to a continuous increase in operating pressures that exceed the critical point of the injected fluids. Especially for supercritical atmospheric conditions with respect to the injected fluid, the fundamental physics of the occurring mixing and evaporation processes are no...

An unsteady analytical solution is proposed to predict the spreading rate of the crown generated by an impacting droplet onto wetted walls. The modelling strategy is based on the direct integration of the boundary layer correction into the potential flow solution that leads to the well-established square-root time dependence. The original potential...

Technology development for propulsion systems of upper stages and reaction control thrusters is driven by green propellants to substitute hydrazine. At high-altitude conditions prior to ignition the liquid propellants are injected into the combustor at near-vacuum. Due to the sudden pressure drop the liquid is in a superheated thermodynamic state r...

High-pressure multi-hole injectors for gasoline direct injection (GDI) engines allow a flexible optimisation of the individual spray hole properties to specific engines and combustion strategies. One degree of freedom within this spray targeting process is the mass flow rate of each spray plume, which is mainly controlled by the corresponding spray...

The surface wettability has a significant influence on the morphology and spreading behavior during droplet impacts on dry smooth walls. On the way for predicting spreading diameters in dependency of the wetting behavior, the experimental database was extended by an experimental study in which distilled water and isopropanol droplets have impacted...

The flourishing of applications in need of self-cleaning mechanisms increased the search for water repellent hydrophobic surfaces with induced roughness. Disclosing the small-scale interface phenomena on the wetting behavior is essential to design efficient hydrophobic materials with defined topography. On the other hand, the spreading behavior con...

Cryogenic supercritical fluids represent an intriguing category of fluids that combine mechanical and thermophysical properties of both ultralow temperature conditions and phenomena taking place well above the critical point. Recent research has demonstrated that it is a common misconception to consider the supercritical state as one homogeneous st...

Mixing and evaporation processes play an important role in fluid injection and disintegration. Laser-induced thermal acoustics (LITA) also known as laser-induced grating spectroscopy (LIGS) is a promising four-wave mixing technique capable to acquire speed of sound and transport properties of fluids. Since the signal intensity scales with pressure,...

The influence of miscibility and liquid wettability during droplet impact onto thin wall films is investigated experimentally. Despite similar liquid properties and impact conditions, differences in the splashing limit, in the crown extension and in the duration of the ascending phase are observed. These differences are related to the interfacial t...

Mixing characteristics of supercritical injection studies were analyzed with regard to the necessity to include diffusive fluxes. Therefore, speed of sound data from mixing jets were investigated using an adiabatic mixing model and compared to an analytic solution. In this work, we show that the generalized application of the adiabatic mixing model...

The present work provides an overview on the possible phase transitions associated with supercritical fluid injection and a detailed evaluation of the mixing process between injectant fluid and quiescent ambience. The experiments cover superheated liquid disintegration, pseudo-boiling transition and single-phase jets under different nozzle pressure...

Due to current and future environmental and safety issues in space propulsion, typical propellants for upper stage or satellite rocket engines such as the toxic hydrazine are going to be replaced by green propellants like the combination of liquid oxygen and hydrogen or methane. The injection of that kind of cryogenic fluids into the vacuum atmosph...

Mean temperatures of acetone, millimeter-sized, freely falling droplets in a nitrogen atmosphere are studied at two different locations downstream a capillary-type injector. Injection and ambient temperatures have been varied independently between 433 and 513 K and pressures from 2 to 6 MPa. The ratio of simultaneously measured laser-induced phosph...

An analytical solution is proposed to predict the crown propagation, generated by a single droplet impact on wetted walls. This approach enables a smooth transition from the inertia-driven to the viscous-controlled regime of crown propagation. The modelling strategy is based on the stagnation-point flow, because it resembles closely the hydrodynami...

The influence of miscibility and liquid wettability during droplet impact onto thin wall films is investigated experimentally. Despite similar liquid properties and impact conditions, differences in the splashing limit, the crown extension and the duration of the ascending phase are observed. These differences are related to the interfacial tension...

The development of new upper orbit thrusters using cryogenic propellants, requires an improved understanding of the dynamics of oxidizer and fuel injection at near vacuum conditions before ignition. Due to the low ambient pressure, the propellants enter a superheated state and flash evaporation occurs. Flash boiling of cryogenic liquid nitrogen is...

During droplet impact on thin wall-films, a liquid lamella, the so-called ‘crown’, expands radially and vertically away from the impact point. This phenomenon is often associated with the growth of fingers at the crown rim, leading to the fascinating crown-type splashing. The present study reports an experimental investigation on droplet impact on...

Drop impact onto wetted surfaces is of relevance to any spray coating application since the maximum spreading diameter and the residual film thickness of the applied liquid droplets affect the efficient distribution of the coating materials. In this paper, we propose a modification to existing models for crown propagation during single drop impact...

Droplet impact on wall-films are typical examples where ‘splashing’, the fragmentation of the crown rim during its expansion, takes place. The triggering instability mechanisms are directly linked to crown rim kinematics. This experimental study analyses which geometrical parameter is physically the most suited for studying crown rim kinematics dur...

The relationship between ‘microscopic’ velocity field and ‘macroscopic’ outcomes of liquid droplet impact on wall-films is not yet fully understood. This article reports a preliminary experimental investigation to measure the velocity field within wall-film when a droplet impacts on it, using micro-Particle Image Velocimetry (μ-PIV). The challenges...

This work analyses whether the inclusion of interfacial temperature jumps is necessary in the modelling of droplet evaporation at high pressure. The analysis is divided into two parts. First, we revise the major findings from theoretical models and molecular dynamics simulations on the conditions leading to the inception of interfacial jumps and th...

The evaporation of liquid drops in stagnant gaseous environment is modelled, accounting for the effect of drop curvature and size at the macro- and microscopic scales. At the macro-scale level, the validity of the conjectured dependence of the local fluxes on the drop surface curvature is analysed. Analytical solutions to the gas-phase conservation...

Influence of liquid miscibility and wettability on the structures produced by drop–jet collisions - Volume 885 - David Baumgartner, Ronan Bernard, Bernhard Weigand, Grazia Lamanna, Günter Brenn, Carole Planchette

Understanding suitable boundary conditions for vapor-liquid interfaces is important for the development of physically realistic simulations of evaporation and condensation processes. This work addresses the question whether the inclusion of interfacial temperature jumps is necessary in the modeling of droplet evaporation or condensation. The analys...

This book provides a selection of contributions to the DIPSI workshop 2019 (Droplet Impact Phenomena & Spray Investigations) as well as recent progress of the Int. Research Training Group “DROPIT”. The DIPSI workshop, which is now at its thirteenth edition, represents an important opportunity to share recent knowledge on droplets and sprays in a va...

For a detailed experimental investigation of superheated cryogenic fluids the new cryogenic test bench M3.3 with a temperature controlled injection system was built at the DLR Institute of Space Propulsion in Lampoldshausen. After a first test campaign with high-speed shadowgraphy of flash boiling liquid nitrogen sprays a Phase Doppler Anemometry s...

Drop impact on a dry/wetted wall is of relevance to many industrial applications as well as to natural sciences. For some applications, such as spray coating or icing of plane wings, both the maximum spreading diameter and the residual thickness of the wall film are of paramount importance for the efficient design and optimisation of the different...

Droplet evaporation within combustion chambers is of high importance for stable and efficient combustion. For ambient pressures exceeding the critical pressure of the injected fuel, evaporation processes are not fully understood yet. Especially the temperature evolution of the injected fuel is a key parameter to understand the transition of near cr...

Experiments and simulations were carried out to contribute to a better understanding and prediction of high-pressure injection into a gaseous environment. Specifically, the focus was put on the phase separation of an initially supercritical fluid due to the interaction with its surrounding. N-hexane was injected into a chamber filled with pure nitr...

In modern gas turbines and internal combustion engines, fluids are injected at high pressures, at fuel states either close to or exceeding the critical point. Accurate prediction of these processes require increasingly precise modelling of evaporating drops. Especially the transition of classical two phase evaporation to single phase dense fluid mixi...

The rapid implementation of Selective-Catalytic-Reduction (SCR) technologies into light passenger and commercial vehicles, led to the omission of fundamental research creating several reliability issues that are largely related to the research field of droplet dynamics. In this study, the splashing behavior of an AdBlue droplet impacting onto thin...

The present work summarises the main findings of a systematic study on the behaviour of liquid droplets embedded in a high pressure and temperature environment. Thanks to the availability of quantitative temperature data, it was possible for the first time to assess the conceptual soundness of different theoretical approaches. In all cases, the pre...

Several diffusion models are compared for their applicability in droplet evaporation modeling over a wide range of temperatures and pressures. Major differences in the physical derivation of the methods are being discussed. Most models being evaluated are only valid for the infinite dilution limit. Additionally they use various numbers of empiricall...

The International Research Training Group GRK 2160/1 was established in October 2016 to focus on droplet interaction technologies. The latter find application in a variety of technological processes, such as spray cooling, coating technologies or the generation of encapsulated material in the pharmaceutical industry. A key feature of this research...

The scenario of an impacting droplet onto a wall-film is highly relevant in many technical systems. In combustion engines, for example, the interaction of fuel drops with oil wall-films can alter the pollutant emissions. In order to make reliable predictions for these systems, it is of crucial importance to gain a deeper insight into the underlying...

Liquid droplet impact on thin wall-films is encountered in a variety of scenarios. Even though there are numerous studies on liquid droplet interaction with wall-films of the same liquid (‘one-component’ interaction), very few studies have considered liquid droplets impacting on wall-films of a different liquid (‘two-component’ interaction). With t...

In this study, n-hexane was compressed beyond six times its critical pressure and discharged into argon at subcritical pressure (with respect to the injectant). The injection temperature systematically varied from sub- to supercritical values to investigate near-critical disintegration phenomena of retrograde jets. Here, the ratio of the pressure i...

We report a comprehensive speed of sound database for multi-component mixing of underexpanded fuel jets with real gas expansion. The paper presents several reference test cases with well-defined experimental conditions providing quantitative data for validation of computational simulations. Two injectant fluids, fundamentally different with respect...

This study is the first to provide a comprehensive speed of sound database for multi-component jet mixing at high pressure. It serves as a unique reference for numerical simulations of mixture preparation processes in future liquid rocket engines and internal combustion engines. We performed quantitative speed of sound measurements in jet mixing zo...

The present paper investigates experimentally the impact dynamics of crown-type splashing for miscible two- and one-component droplet wall–film interactions over a range of Weber numbers and dimensionless film thicknesses. The splashing outcome is parametrised in terms of a set of quantifiable parameters, such as crown height, top and base diameter...

The disintegration process of liquid fuel within combustion chambers is one of the most important parameters forefficient and stable combustion. Especially for high pressures exceeding the critical value of the injected fluids the mixing processes are not fully understood yet. Recently, different theoretical macroscopic models have been introduced...

Experiments and numerical simulations were carried out in order to contribute to a better understanding and predic-tion of high-pressure injection into a gaseous environment. Specifically, the focus was put on the phase separation processes of an initially supercritical fluid due to the interaction with its surrounding. N-hexane was injected into a...

Single drop impacts on thin liquid layers are of particular interest because of the ejection of secondary droplets, the so-called splashing. Only a few studies handle the deposition/splashing limit for two-component interaction, where the liquid properties of the impacting drop and wall film differ significantly. This study aims at identifying a un...

Experiments and numerical simulations were carried out in order to contribute to a better understanding and prediction of high-pressure injection into a gaseous environment. Specifically, the focus was put on the phase separation processes of an initially supercritical fluid due to the interaction with its surrounding. N-hexane was injected into a...

An electrohydrodynamic model for the simulation of droplet formation, motion and detachment in an electrically driven droplet generator is introduced. The numerical approch is based on the coupled solution of the multiphase flow problem with the charge continuity equation. A conduction-convection model, taking into account conductive , capacitive a...

An electrohydrodynamic model for the simulation of droplet formation, detachment and motion in an electrically driven droplet generator is introduced. The numerical approach is based on the coupled solution of the multiphase flow problem with the charge continuity equation. For the latter, a modified convection-conduction model is applied, taking i...

The four-wave mixing technique laser-induced thermal acoustics was used to measure the local speed of sound in the farfield zone of extremely underexpanded jets. N-hexane at supercritical injection temperature and pressure (supercritical reservoir condition) was injected into quiescent subcritical nitrogen (with respect to the injectant). The techn...

The phenomenon of a single drop impact onto a thin liquid film (e.g. wall-film) is encountered over a wide range of natural and engineering applications. Among different drop impact morphologies, splashing has drawn great attention over the last decades due to its relatively complex morphology that is characterised by liquid fingers at the upper cr...

In typical passenger car diesel engines, multi-hole nozzles with small diameters are advantageous under low and part load conditions due to improved atomization and faster evaporation of the injected fuel. In contrast, nozzles with larger diameters are needed at full load in order to rapidly inject larger quantities of fuel and to mix them with air...

To meet stringent emission legislation, passenger cars with direct gasoline injection require fast atomization of the injected fuel and rapid, complete mixture formation. In order to reach these goals, higher injection pressures up to 300 bar will be used in the foreseeable future. However, an increase of the pressure level is costly and raises dem...

Rising pressures in modern combustion systems lead to conditions that can be supercritical for the injected liquid fuels. Quantitative measurement data is required for a better understanding of this complex process and for validation of corresponding simulations. The present study focusses on the evaporation of single free-falling droplets to reduc...

Non-resonant laser-induced thermal acoustics (LITA), a four-wave mixing technique, was applied to post-shock flows within a shock tube. Simultaneous single-shot determination of temperature, speed of sound and flow velocity behind incident and reflected shock waves at different pressure and temperature levels are presented. Measurements were perfor...

This paper investigates the morphology of a flash-atomizing jet at conditions representative for rocket engine operations. Due to its relevance for the aerospace industry, both storable and cryogenic rocket engine propellants are considered, namely ethanol [as inert equivalent of monomethyl hydrazine (MMH)] and liquid oxygen (LOx). A comparison bet...

The present paper discusses some preliminary experimental results on the droplet size and temperature distributions in superheated sprays. Droplet size data show that liquid disintegration controlled by nucleate boiling is less efficient compared to aerodynamic-controlled atomization. In fact, it leads to larger SMD values. The size distribution ev...